The Solar System

The words " solar system" refer to the Sun and all of the objects
that travel around it. These objects include planets, natural satellites such
as the Moon, the asteroid belt, comets, and meteoroids. Our solar system has
an elliptical shape and is part of a galaxy known as the Milky Way. The Sun is
the center of the solar system. It contains 99.8% of all of the mass in
our solar system. Consequently, it exerts a tremendous
gravitational pull on planets, satellites, asteroids, comets, and
meteoroids.
Astronomers believe the solar system formed 4.5 billion years ago.
However, they differ in their beliefs about how the system formed. Some
believe the whole solar system formed from a single flat cloud of gas, while
others believe it formed when a huge object passed near the Sun, pulling a
stream of gas off of the Sun. Astronomers theorize the planets then formed
from this gas stream.